1. Field of the Invention
This invention relates generally to reverse flow cooled dynamoelectric machines and more specifically to an arrangement for cooling the end turns of the rotor winding of such machines.
2. Description of the Prior Art
Large dynamoelectric machines such as turbine-generators are pressurized with a cooling gas such as hydrogen which is pumped throughout the machine by a fan fixed to the rotor. The cooling gas is pumped by the fan through cooling passages in a laminated stator core and into a gas gap defined by the interior of the stator core and the rotor surface. Cooling gas may be picked up by the rotor at its outer surface in a manner described in U.S. Pat. No. 3,348,081 D. M. Willyoung and pumped through cooling passages defined by the field coils within the rotor, such structure being shown in U.S. Pat. No. 2,986,664 to D. M. Willyoung and P. A. Becker.
One particular cooling system employed in dynamoelectric machines is known as reverse flow cooling, an example of which is disclosed and claimed in U.S. Pat. No. 3,739,208 to Shartrand, assigned to the assignee of the present invention. In a reverse flow cooling system such as that shown in the aforementioned Shartrand patent, cooling gas is drawn from the end of the gas gap into the fan and is pumped by the fan to one or more gas coolers usually located in the upper portion of the machine. From the gas cooler, the flow of cooling gas is split, a portion of it being channeled to the interior of an end portion of the rotor, and the remainder being channeled into cooling passages disposed within the laminations of the stator core. The fan is normally mounted on a fan ring fixed to a spindle of the rotor.
The cooling gas channeled to the interior of the rotor is pumped thereinto through gas passages machined in the rotor spindle and extending from the fan ring to the end turns of the rotor winding. If the fan ring is shrunk on the spindle, the passages may be milled out of the rotor forging in an axial direction. However, on one end of the dynamoelectric machine rotor, there is provided a coupling to connect the rotor to a driving turbine. This coupling is of a diameter too large to allow a fan ring to pass over the coupling and be shrunk on the spindle. Therefore, at the turbine end of the rotor it is necessary to form the fan ring integral with the spindle. To provide the gas passages through which cooling gas is pumped to the end turns of the rotor winding, it is necessary to bore or drill through the fan ring. However, the turbine coupling interferes with the axial boring or drilling of the passages.
That portion of the gas channeled to the dynamoelectric machine rotor from the gas cooler impinges upon the fan ring in entering the cooling passages which provide for the conduction of the gas to the end turns of the rotor winding. Under the conditions of normal operation, the rotating fan ring imparts a tangential component of velocity to that cooling gas, that is, a component transverse to the direction of movement of the gas as it approaches the fan ring. Therefore, when longitudinal passages, that is, passages extending parallel to the axis of the rotor, are employed, substantial pressure losses occur in the gas flow since the direction of these passages differs from the direction in which the gas is being urged by the velocity imparted thereto.
By the present invention, the above problems associated with the prior art are avoided and an approach is provided in which the rotor gas passages through which the cooling gas is pumped to the end turns of the rotor winding extend in a direction which matches, to the most practicable extent, the direction of the cooling gas flow entering the passages. Further, the passages are provided in a direction which enables them to be formed by drilling or boring through the fan ring and a portion of the rotor spindle without interference from the turbine coupling.
Accordingly, it is an object of the present invention to provide a reverse flow cooled dynamoelectric machine with cooling gas passages extending from the fan ring to the end turns of the rotor winding in a direction which reduces or minimizes pressure losses in the flow of gas.
It is another object of the present invention to provide a dynamoelectric machine with rotor cooling gas passages which may be formed by boring or drilling through the fan ring without interference from the turbine coupling.